Tidy up #redirect_to_payment_gateway

app/controllers/checkout_controller.rb

@@ -191,17 +191,19 @@ class CheckoutController < ::BaseController
   end
 
   def redirect_to_payment_gateway
-    payment_method_id = params.dig(:order, :payments_attributes, 0, :payment_method_id)
-    payment_method = Spree::PaymentMethod.find(payment_method_id)
-
-    redirect_url = payment_method&.external_payment_url(order: @order)
-
-    return if redirect_url.blank?
+    return unless selected_payment_method.external_gateway?
+    return unless (redirect_url = selected_payment_method.external_payment_url(order: @order))
 
     render json: { path: redirect_url }, status: :ok
     true
   end
 
+  def selected_payment_method
+    @selected_payment_method ||= Spree::PaymentMethod.find(
+      params.dig(:order, :payments_attributes, 0, :payment_method_id)
+    )
+  end
+
   def order_error
     if @order.errors.present?
       @order.errors.full_messages.to_sentence

spec/controllers/checkout_controller_spec.rb

@@ -423,6 +423,7 @@ describe CheckoutController, type: :controller do
 
       it "should call Stripe redirect and redirect if a path is provided" do
         expect(Spree::PaymentMethod).to receive(:find).and_return(payment_method)
+        expect(payment_method).to receive(:external_gateway?).and_return(true)
         expect(payment_method).to receive(:external_payment_url).and_return("test_path")
 
         spree_post :update,